Immune responses to varicella-zoster (V-Z) virus will be examined in man, the only known host for V-Z virus. Responses in patients who are immune and susceptible to varicella will be studied; some of these patients will be healthy while others will be immunocompromised. Whole blood will be obtained from patients, and the serum will be tested for humoral antibody to V-Z virus. The white blood cells will be separated on density gradients into T and B lymphocytes and monocytes (macrophage precursors). The ability of these cells, singly and in combination, to inactivate C-Z virus in tissue culture will be studied. The influence of antibody on the inactivation will also be studied. The ability of white blood cells to support the growth of V-Z virus will be tested. A search for a lymphocyte mediator against V-Z will be made, and if a mediator is found, an attempt to determine whether it is an interferon will be made. In clinical studies an attempt to passively immunize patients at high risk to the development of varicella will be made. While Zoster Immune Globulin (ZIG) is efficacious for this purpose, it is frequently unavailable for those who need it. For this reason passive immunization with Immune Serum Globulin (ISG) of known high titer of antibody will be used. ISG will be given in small doses prior to exposure and in large doses following exposure. Antibody titers before and after administration of ISG will be monitored. ISG will be given only to patients for whom ZIG is unavailable.